Regulatory Matters - GPC Nuclear Construction (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2012 utility MW	Aug. 31, 2018
Loss Contingencies [Line Items]
Estimated loss on Plant Vogtle Units 3 and 4	$ 48	$ 0
GEORGIA POWER CO
Loss Contingencies [Line Items]
Estimated loss on Plant Vogtle Units 3 and 4	48	$ 0
Estimated loss on Plant Vogtle Units 3 and 4, net of tax	$ 36
GEORGIA POWER CO | Plant Vogtle Units 3 And 4
Loss Contingencies [Line Items]
Proportionate ownership share	45.70%
Number of construction units approved | utility			2
Electric generating capacity in mega watts under consortium agreement | MW			1,100
Estimated cost to complete, construction contingency estimate, financing costs	$ 3,000
Estimated cost to complete, construction contingency estimate, financing costs, incurred to date	2,700
Construction contingency estimate	84
Construction contingency estimate, additional amount	48
Base project capital cost forecast, monthly	25
Monthly AFUDC	$ 15
Percentage of ownership interest required for voting for continuing construction				90.00%
GEORGIA POWER CO | Plant Vogtle Units 3 And 4 | Vogtle Owners
Loss Contingencies [Line Items]
Period of notice required in the event letters of credit are not renewed	30 days
Minimum | GEORGIA POWER CO | Plant Vogtle Units 3 And 4 | COVID-19
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss, loss of productivity, term	3 months
Estimate of possible loss	$ 150
Maximum | GEORGIA POWER CO | Plant Vogtle Units 3 And 4 | COVID-19
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss, loss of productivity, term	4 months
Estimate of possible loss	$ 190